Definition
The moral zeitgeist is the broad, shared set of moral attitudes that prevails in a society at a particular moment — the unspoken consensus about what is acceptable, admirable, or unthinkable. Zeitgeist is German for "spirit of the age."
The striking feature of the moral zeitgeist is that it moves. Practices once widely accepted come to be seen as wrong, and concerns once ignored become matters of conscience. The consensus of one generation is not the consensus of the next.
Why it matters
How it works
Dawkins uses the moral zeitgeist to make a specific argument: if our morality were drawn directly from an unchanging scripture, it would not drift the way it plainly does. Believers and non-believers alike now reject practices that older texts tolerate, which suggests an independent moral sense is steering the selection.
The mechanism behind the drift is itself an open question. Dawkins points to improved discourse, wider education, and the spread of ideas, while acknowledging that no one fully accounts for the change.